PROJECT SUMMARY Human papillomavirus positive (HPV+) oropharyngeal squamous cell carcinoma (OPSCC) is increasing in incidence, particularly among younger individuals. About 85% of these patients respond well to the current standard-of-care treatments that include radiotherapy (XRT), but many have high morbidity due to long-term treatment related side effects. De-escalation protocols have been proposed, and are being evaluated, in order to reduce treatment-related morbidity without compromising the observed high survival rates. However, some patients exhibit poor response to standard therapy, making the implementation of de-escalation protocols challenging. The good outcomes among HPV+ OPSCC patients are believed to be determined by their higher response to XRT, but the reasons for lack of response among some individuals are unknown. There is an urgent need to develop biomarkers for identification of treatment resistant individuals. This would allow safe implementation of de-intensification protocols for low risk patients, and discovery of alternative therapeutics for treatment resistant patients. HPV+ OPSCC is genomically distinct from HPV negative tumors, and recent studies have characterized the spectrum of genomic alterations in these tumor types. However, these genomic analyses have not led to the clinical implementation of any genomic or molecular biomarkers for HPV+ OPSCC. We have analyzed genomic data from The Cancer Genome Atlas (TCGA) project for genes related to HPV function and identified a signature for poor outcome in HPV+ OPSCC. This signature is robust across multiple validation cohorts and is associated with XRT resistance in cell lines. We hypothesize that this signature identifies an important and new aspect of HPV biology that can be utilized for patient stratification and treatment personalization. We propose to optimize this biomarker signature for clinical use, use the underlying biology to understand the mechanisms driving sensitivity to XRT, and test new approaches to sensitize HPV+ tumors to XRT.